General Information about Tachinid Flies

by James E. O'Hara

The Tachinidae are a large and diverse family of flies (Diptera) consisting of about 10,000 described species worldwide and about 1400 described species in America north of Mexico. Perhaps several thousand species remain to be described, particularly in the tropics. Adult tachinids range in size from 2 mm to over 20 mm and display a wide variety of shapes, colours and sizes. They can be separated from most other flies by the presence of a well developed subscutellum (postscutellum) and a row of setae on the meron (hypopleuron) (see Tachinid Morphology).

Tachinid ovipositing on Japanese beetles

Female tachinid fly, Istocheta aldrichi (Mesnil), ovipositing on a mating pair of Japanese beetles, Popillia japonica (Newman).
Photo from frontispiece of an article on the Japanese beetle by Clausen et al., 1927, USDA Dept. Bul. 1429, 55 pp.

All tachinids are internal parasitoids of other arthropods during their larval stage. Hosts are primarily immatures of moths, sawflies and beetles, and adults of beetles and bugs. Hosts include many of the major insect pests of economic concern to the agricultural and forestry industries in Canada. Since hosts are usually killed by their tachinid parasitoids and tachinids have rather narrow host preferences, tachinid flies constitute an important resource in terms of biological control of pest insects. Naturally-occurring species help keep populations of potential insect pests in check, while certain exotic species have been introduced into North America as part of biological control programs aimed at controlling targeted pests.

Tachinid fly (Winthemia sp.) ovipositing on whitelined sphinx moth, Hyles lineata (Fabricius).
Photo courtesy of Robert W. Mitchell.

Tachinid ovipositing on whitelined sphinx moth

Tachinid flies are not well known at the species level in America north of Mexico. Though the number of species described probably accounts for 80-90% of the total number of species in the region, few keys are available to distinguish them. It is estimated that less than 20% of the species in America north of Mexico can be reliably keyed. Consequently, almost all species identifications depend on comparisons, by a specialist, of unidentified specimens with previously identified museum specimens.

Mating pair of Aphantorhaphopsis samarensis (Villeneuve), a European parasitoid of the gypsy moth, Lymantria dispar (L.).
Photo courtesy of International Institute of Biological Control, Delémont.

For information on the classification and biology of the Tachinidae of America north of Mexico, see:

Wood, D.M. 1987. Chapter 110. Tachinidae. Pp. 1193-1269. In McAlpine, J.F., et al., Manual of Nearctic Diptera. Volume 2. Agriculture Canada Monograph 28.

For host information on the Tachinidae of America north of Mexico, see:

Arnaud, P.H., Jr. 1978. A host-parasite catalog of North American Tachinidae (Diptera). United States Department of Agriculture, Miscellaneous Publication 1319: 1-860.

First published on the Internet in 1997
Last update: 20 June 2003
J.E. O'Hara